H94: Ensuring that elements do not contain duplicate attributes

Applicability

Description

The objective of this technique is to avoid key errors that are known
to cause problems for assistive technologies when they are trying to
parse content that has duplicate attributes on the same element. This
can be checked manually, or by using HTML's mechanism to specify the
technology and technology version and validating the document for this
condition. There are several validators that the developer can use;
validation reports generally mention this type of error. The document
type declaration is not strictly necessary for this type of evaluation,
but specifying the document type declaration makes it easier to use
a validator.

Examples

Example 1: HTML Validators

HTML pages include a document type declaration (sometimes referred
to as !DOCTYPE statement). The developer can use offline or online
validators (see Resources below) to check that attributes are only
used once on an element. The W3C validador, for example, will report "duplicate
specification of attribute X" when it encounters the second definition
of the same attribute on an element.

Tests

Procedure

Check that no attribute occurs more than once on any element

Expected Results

Check 1 is true.

If this is a sufficient technique for a success criterion, failing this test procedure does not necessarily mean that the success criterion has not been satisfied in some other way, only that this technique has not been successfully implemented and can not be used to claim conformance.

Techniques are Informative

Techniques are informative—that means they are not required. The basis for determining conformance to WCAG 2.0 is the success criteria from the WCAG 2.0 standard—not the techniques. For important information about techniques, please see the Understanding Techniques for WCAG Success Criteria section of Understanding WCAG 2.0.